This invention relates generally to biomedical and/or pharmaceutical applications of absorbable or biodegradable polymeric hydrogels. More particularly, the present invention relates to hydrogel-forming, self-solvating, absorbable polyester copolymers capable of selective, segmental association into compliant hydrogels upon contacting an aqueous environment. The invention also discloses methods of using the polyester copolymers of the invention in humans for providing a protective barrier to prevent post-surgical adhesion, a carrier of viable cells or living tissue, treatment of defects in conduits such as blood vessels, and controlled release of a biologically active agent for modulating cellular events such as wound healing and tissue regeneration or therapeutic treatment of diseases such as cancer and infection of the periodontium, eye, dry socket, bone, skin, vaginal, and nail infections.
Hydrogels are materials which absorb solvents (such as water), undergo rapid swelling without discernible dissolution, and maintain three-dimensional networks capable of reversible deformation (Park, et al., Biodegradable Hydrogels for Drug Delivery, Technomic Publishing Co., Lancaster, Pa., 1993; W. Shalaby et al., J. Controlled Rel., 19, 131, 1992; and Silberberg, in Molecular Basis of Polymer Networks (Baumgartner, A. and Picot, C. E., Eds.), Spring-Verlag, Berlin, 1989, p. 147).
Covalently crosslinked networks of hydrophilic polymers, including water-soluble polymers are traditionally denoted as hydrogels (or aquagels) in their hydrated state. Hydrogels have been prepared to be based on crosslinked polymeric chains of methoxy poly(ethylene glycol) monomethacrylate having variable lengths of the polyoxyethylene side chains, and their interaction as hydrogels, with blood components have been studied (Nagaoka, et al., in Polymers as Biomaterials (Shalaby, S. W., et al., Eds.), Plenum Press, 1983, p. 381). A number of aqueous hydrogels (aquagels) have been used in various biomedical applications, such as, for example, soft contact lenses, wound management, and drug delivery. However, methods used in the preparation of these hydrogels, and their conversion to useful articles, are subject to the constraints associated with the nature of their three-dimensional thermosetting structures and, hence, deprive the users from applying the facile processing techniques employed in the production of non-crosslinked thermoplastic materials.
This, and the low mechanical strength of the hydrated networks, led a number of investigators to explore the concept of combining hydrophilic and hydrophobic polymeric components in block (Okano, et al., J. Biomed. Mat. Research, 15, 393, 1981), or graft copolymeric structures (Onishi, et al., in Contemporary Topics in Polymer Science, (W. J. Bailey and T. Tsuruta, eds.), Plenum Publ. Co., New York, 1984, p. 149), and blends (Shah, Polymer, 28, 1212,1987; and U.S. Pat. No. 4,369,229) to form the xe2x80x9chydrophobic-hydrophilicxe2x80x9d domain systems, which are suited for thermoplastic processing (Shah, Chap. 30, in Water Soluble Polymers (S. W. Shalaby, et al., Eds.), Vol. 467, ACS-Symp. Ser., Amer. Chem. Soc., Washington, 1991). The xe2x80x9chydrophobic-hydrophilicxe2x80x9d domain system (HHDS) undergoes morphological changes which are associated with the hydration of the hydrophilic domains and formation of pseudo-crosslinks via the hydrophobic component of the system (Shah, 1991, cited above). Such morphology was considered to be responsible for the enhanced biocompatibility and superior mechanical strength of the two-phase HHDS as compared to those of covalently crosslinked, hydrophilic polymers. The mechanism of gel formation in the present invention parallels that described by Shah, 1991, cited above, for non-absorbable blends of hydrophilic-hydrophobic domain systems (HHDS). However, differences exist between the copolymers of the present invention, and more particularly, Component xe2x80x9cAxe2x80x9d, and HHDS. In this regard, Component A is based on a water-soluble and water-insoluble block structure (SIBS). This is not a mere physical mixture of two polymers as are the blends described by Shah, 1991, cited above. Additionally, due to the presence of covalent links between the blocks of SIBS, the resulting hydrogel displays higher elasticity compliance and tensile strength while being absorbable. In fact, the SIBS systems are, in some respects, analogous to thermoreversible gels (Shalaby, in Water-Soluble Polymers, (Shalaby, S. W., et al., Eds.), Vol. 467, Chapt. 33, ACS Symp. Ser., Amer. Chem. Soc., Washington, DC, 1991a) in displaying a hydration-dehydration equilibrium governing the system transformation, i.e., the gel/liquid equilibrium is driven by the water content of the SIBS. Thus, in the absence of water, the polyoxyalkylene blocks undergo intermolecular segmental mixing with the neighboring hydrophobic blocks to produce a viscous liquid. In the presence of water, competition between the water as an extrinsic solvent and the polyester block for the polyoxyalkylene (POA) block forces the hydration of the POA, and aggregation or association of the polyester blocks to establish pseudo-crosslinks which maintain a 3-dimensional integrity. Since gel formation takes place in an aqueous environment, the POA block will preferentially migrate to the exterior of the gel and interface with the adjoining tissues to establish an adhesive joint, which prevents gel migration from target site and sustains its intended efficacy. As for example, for periodontal and dry socket applications, post-surgical adhesion prevention and treatment of vaginal and bone infections, and other applications where predictable site residence of the gel cannot be compromised.
Synthesis and biomedical and pharmaceutical applications of absorbable or biodegradable hydrogels based on covalently crosslinked networks comprising polypeptide or polyester components as the enzymatically or hydrolytically labile components, respectively, have been described by a number of researchers (Jarrett, et. al., Trans. Soc. Biomater., Vol. XVIII, 182, 1995; Pathak, et. al., Macromolecules, 26, 581, 1993; Park, et. al., Biodegradable Hydrogels for Drug Delivery, Technomic Publishing Co., Lancaster, Pa., 1993; Park, Biomaterials, 9, 435, 1988; and W. Shalaby, et. al., 1992, cited elsewhere herein). The hydrogels most often cited in the literature are those made of water-soluble polymers, such as polyvinyl pyrrolidone, which have been crosslinked with naturally derived biodegradable components such as those based on albumin (Park, et. al., 1993, cited elsewhere herein; and W. Shalaby, et. al., 1992, cited elsewhere herein). Totally synthetic hydrogels which have been studied for controlled drug release and membranes for the treatment of post-surgical adhesion are based on covalent networks formed by the addition polymerization of acrylic-terminated, water-soluble chains of polyether dl-polylactide block copolymers (Jarrett, et. al., 1995, cited elsewhere herein; and Pathak, et al., 1993, cited elsewhere herein).
Polymer solutions which undergo reversible gelation by heating or cooling about certain temperatures (lower critical solution temperature, LCST) are known as thermoreversible gels. Theoretical and practical aspects of key forms of thermoreversible gels are described by Shalaby, 1991a, cited elsewhere herein. Among the thermoreversible gels discussed by Shalaby are those of amorphous N-substituted acrylamides in water and amorphous polystyrene and crystalline poly(4-methyl pentene) in organic solvents. Prevailing gel formation mechanisms include molecular clustering of amorphous polymers and selective crystallization of mixed phases of crystalline materials. Thermodynamic parameters (enthalpy and entropy) which favor gel formation in terms of LCST are discussed by Shalaby only with respect to the solvent-polymer interaction. Shalaby fails, however, to address self-solvating chains.
U.S. Pat. No. 4,911,926, discloses aqueous and non-aqueous compositions comprised of block polyoxyalkylene copolymers that form gels in the biologic environment, for preventing post-surgical adhesion. Other gel forming compositions for use in preventing post-surgical adhesion include: (a) chitin derivatives (U.S. Pat. No. 5,093,319); (b) aqueous solutions of xanthan gum (U.S. Pat. No. 4,994,277); (c) chitosan-coagulum (U.S. Pat. No. 4,532,134); and (d) hyaluronic acid (U.S. Pat. No. 4,141,973).
Absorbable polymers, or often referred to as biodegradable polymers, have been used clinically in sutures and allied surgical augmentation devices to eliminate the need for a second surgical procedure to remove functionally equivalent non-absorbable devices (U.S. Pat. No. 3,991,766, to Schmitt et al.; and Shalaby, in Encyclopedia of Pharmaceutical Technology (J. C. Boylan and J. Swarbrick, eds.), Vol. 1, Dekker, New York, 1988, p. 465). Although these devices were designed for repairing soft tissues, interest in using such transient systems, with or without biologically active components, in dental and orthopedic applications has grown significantly over the past few years. Such applications are disclosed in Bhatia, et. al., J. Biomater. Sci., Polym. Ed., 6(5), 435, 1994; U.S. Pat. No. 5,198,220, to Damani; U.S. Pat. No. 5,198,220, to Wasserman, et. al.; and U.S. Pat. No. 3,991,766, to Schmitt et al.
U.S. Pat. No. 3,991,766, to Schmitt et al., discloses absorbable articles made of polyglycolide, such as sutures, clips and storage pallets having medicaments incorporated therein and can be used for both their own mechanical properties and delayed release systems of medicaments. U.S. Pat. No. 5,171,148, to Wasserman et al., discloses the use of absorbable polymers made from p-dioxanone or L-lactide and glycolide as dental inserts for the treatment of periodontal disease. Here, a semiporous mesh material with sealed edges is emplaced between the tooth and gingiva. The implant is attached to the tooth by an absorbable ligature material. U.S. Pat. No. 5,198,220, to Damani, discloses the treatment of periodontal disease through the use of a sustained release composition/device comprising bioactive agents. The composition/device is in a liquid, semi-solid or solid form suitable for insertion into or around the periodontal pocket. Damani also teaches the formation of a gel, or paste, composition consisting of poly(lactyl-co-glycolide) in an acceptable solvent (such as propylene carbonate), with or without propylene and/or polyethylene glycol, and an antibiotic agent such as tetracycline hydrochloride.
Other in-situ forming biodegradable implants and methods of forming them are described in U.S. Pat. Nos. 5,278,201 (""201 Patent) and 5,077,049 (""049 Patent), to Dunn et al. The Dunn et al., patents disclose methods for assisting the restoration of periodontal tissue in a periodontal pocket and for retarding migration of epithelial cells along the root surface of a booth. The ""049 Patent discloses methods which involve placement of an in-situ forming biodegradable barrier adjacent to the surface of the tooth. The barrier is microporous and includes pores of defined size and can include biologically active agents. The barrier formation is achieved by placing a liquid solution of a biodegradable polymer, such as poly(dl-lactide-co-glycolide) water-coagulatable, thermoplastic in a water miscible, non-toxic organic solvent such as N-methyl pyrrolidone (i.e., to achieve a typical polymer concentration of xe2x89xa650%) into the periodontal pocket. The organic solvent dissipates into the periodontal fluids and the biodegradable, water coagulatable polymer forms an in-situ solid biodegradable implant. The dissipation of solvent creates pores within the solid biodegradable implant to promote cell ingrowth. The ""859 Patent likewise discloses methods for the same indications involving the formation of the biodegradable barrier from a liquid mixture of a biodegradable, curable thermosetting prepolymer, curing agent and water-soluble material such as salt, sugar, and water-soluble polymer. The curable thermosetting prepolymer is described as an acrylic-ester terminated absorbable polymer.
The ""049 and ""859 Patents, as well as U.S. Pat. No. 4,938,763 to Dunn et al., disclose polymer compositions primarily consisting of absorbable thermoplastic or thermosetting polymer, dissolved in organic solvent. These compositions are also described to produce, in an aqueous environment, solids which can be used as tissue barrier (Fujita, et. al., Trans. Soc. Biomater., Vol. XVII, 384, 1994) substrate for tissue generation (Dunn, et. al., Poly. Prepr., 35(2), 437, 1994a) or carrier for the controlled delivery of drugs (Sherman, et. al., Pharm. Res., 11(10 5-318, 1994). Acrylate-endcapped poly(caprolactone) prepolymer was also used as a branched precursor for the in-situ formation of a crosslinked system for potential use in controlled drug release (Moore, et. al., Trans. Soc. Biomater., Vol. XVIII, 186, 1995).
A number of controlled delivery systems for the treatment of periodontal disease are also described in the literature. For example, U.S. Pat. No. 4,919,939, to Baker, discloses a controlled release delivery system for placement in the periodontal pocket, gingival sulcus, tooth socket, wound or other cavity within the mouth. The system incorporates microparticles in fluid medium and is effective in the environment of use for up to 30 days. The drug, in 10-50 micron polymer particles, is released at a controlled rate by a combination of diffusion of the drug through the polymer and erosion of the polymer.
U.S. Pat. No. 5,135,752, to Snipes, discloses a buccal dosage form, which melts in the oral cavity, yet will not spontaneously deform at higher temperatures encountered in shipment and storage. This composition comprises two grades of polyethylene glycol, polyethylene oxide, long-chain saturated fatty acid, and colloidal silica.
U.S. Pat. No. 5,366,733, to Brizzolars et al., discloses an oral composition for the local administration of a therapeutic agent to a periodontal pocket comprising at least one therapeutic agent dispersed in a matrix including a biocompatible and/or biodegradable polymer. The composition is administered as a plurality of dry discrete microparticles, said microparticles are prepared by a phase separation process. An oral composition is also described wherein the polymer comprises a block copolymer of polyglycolide, trimethylene carbonate and polyethylene oxide. Apparatus and methods are also provided for dispensing the dry microparticles to the periodontal pocket, whereby they become tacky and adhere to the involved tissue so as to induce long-term therapeutic effects.
In addition, a number of systems for the controlled delivery of biologically active compounds to a variety of sites are disclosed in the literature. For Example, U.S. Pat. No. 5,011,692, to Fujioka et al., discloses a sustained pulsewise release pharmaceutical preparation which comprises drug-containing polymeric material layers. The polymeric material layers contain the drug only in a slight amount, or free of the drug. The entire surface extends in a direction perpendicular to the layer plane and is coated with a polymeric material which is insoluble in water. These types of pulsewise-release pharmaceutical dosages are suitable for embedding beneath the skin.
U.S. Pat. No. 5,366,756, to Chesterfield et al., describes a method for preparing porous bioabsorbable surgical implant materials. The method comprises providing a quantity of particles of bioabsorbable implant material, and coating particles of bioabsorbable implant material with at least one growth factor. The implant can also contain antimicrobial agents.
U.S. Pat. No. 5,385,738, to Yamahira et al., discloses a sustained-release injection system, comprising a suspension of a powder comprised of an active ingredient and a pharmaceutically acceptable biodegradable carrier (e.g., proteins, polysaccharides, and synthetic high molecular weight compounds, preferably collagen, atelo collagen, gelatin, and a mixture thereof) in a viscous solvent (e.g., vegetable oils, polyethylene glycol, propylene glycol, silicone oil, and medium-chain fatty acid triglycerides) for injection. The active ingredient in the pharmaceutical formulation is incorporated into the biodegradable carrier in the following state: (i) the active ingredient is chemically bound to the carrier matrix; (ii) the active ingredient is bound to the carrier matrix by intermolecular action; or (iii) the active ingredient is physically embraced within the carrier matrix.
Furthermore, a common complication which is encountered by many surgeons following tooth extraction is dry socket. Dry socket occurs following three to four percent of routine extractions (Field, et. al., J. Oral Maxillofac. Surg., 23(6), 419, 1985), and its etiology appears to be multifactorial (Westerholm, Gen. Dent., July-Aug., 306, 1988). Over the years, dry socket has been referred to as alveoloalgia, alveolitis sicca dolorosa, avascular socket, localized osteitis, fibrinolytic alveolitis and localized acute alveolar osteomyelitis (Shafer, et al., A Textbook of Oral Pathology, 4th Ed., W. B. Saunders Co., Philadelphia, 1974, p. 605, 1974; and Birn, Int. J. Oral Sureg., 2, 211, 1973). Although many chemotherapeutic prevention measures or management have been pursued, none have significantly reduced the incidence of dry socket (Birn, 1973, cited above; Field, et. al., 1985, cited above). Among such approaches to the therapeutic treatment of dry socket, with limited success, are those based on systemic administration of antibiotics (Westerholm, 1988, cited above) or direct placement of powdered sulfadiazine or sulfathiazole into the socket (Elwell, J. Amer. Dent. Assoc., 31, 615, 1944).
To date, the known HHDS and thermoreversible gels can be classified as non-absorbable materials and are expected not to absorb through chain dissociation in the biological environment. Meanwhile, there is a growing interest in developing absorbable sutures and allied surgical devices such as transient implants, which are degraded to bioabsorbable, safe by-products and leave no residual mass at the surgical site, as well as frequently cited clinical advantages (Shalaby, Chap. 3 in High Technology Fibers (M. Lewin and J. Preston, eds.), Dekker, New York, 1985; Shalaby, 1988, cited elsewhere herein; Shalaby, Polym. News, 16, 238, 1991; Shalaby, J. Appl. Biomater., 3, 73, 1992; Shalaby, Biomedical Polymers: Designed to Degrade Systems, Hanser Publ., New York, 1994; and Shalaby, et al, eds. Polymers of Biological and Biomedical Significance, Vol. 520, ACS-Symp. Ser., Amer. Chem. Soc., Washington, 1993) have justified the need for novel absorbable hydrogel formulations.
Moreover, such systems as those previously described in the literature, for example, such as by Dunn, et al, (U.S. Pat. No. 4,938,763), teach in-situ formations of biodegradable, microporous, solid implants in a living body through coagulation of a solution of a polymer in an organic solvent such as N-methyl-2-pyrrolidine. However, the use of solvents, including those of low molecular organic ones, facilitates migration of the solution from the application site thereby causing damage to living tissue including cell dehydration and necrosis. Loss of the solvent mass can lead to shrinkage of the coagulum and separation from surrounding tissue.
Furthermore, currently available drug delivery systems deal with solid implants which can elicit mechanical incompatibility and, hence, patient discomfort. The present invention provides novel, hydrogel-forming copolymers, which in contrast to those systems previously described, are absorbable, do not require the use of solvents, and are compliant, swollen, mechanically compatible gels, which adhere to surrounding tissue.
The primary object of the present invention is to provide a hydrogel-forming, self-solvating, absorbable polyester copolymer capable of selective, segmental association into a compliant hydrogel mass on contact with an aqueous environment.
Another object of the present invention, is to provide such a copolymer optionally comprising a biologically active agent.
Yet another object of the present invention, is to provide such a copolymer optionally comprising a low molecular weight component.
A further object of the present invention, is to provide such a copolymer capable of the controlled-release of a biologically active agent/drug for modulating cellular events, such as, wound healing and tissue regeneration.
A further object of the present invention, is to provide such a copolymer capable of the controlled-release of a biologically active agent/drug for therapeutic treatment of diseases, such as, cancer and infection of the, eye, oral cavity, dry socket, bone, skin, vaginal and nail infections.
A further object of the present invention, is to provide such a copolymer which is capable of being extruded or injected into living tissue, or onto the surface thereof, for providing a protective barrier with or without an anti-inflammatory agent or an agent which inhibits fibrotic tissue production for treating conditions, such as, post-surgical adhesion.
A further object of this invention is to provide such a copolymer for constituting or constructing a carrier of peptides or proteins, vaccines, living cells, or viable tissue for sustaining biological functions both in vitro and in vivo.
A further object of the present invention, is to provide such a copolymer which is capable of acting as a blocking agent or sealant for treating defects in conduits.
Accordingly, the present invention provides hydrogel-forming, self-solvating, absorbable polyester copolymers capable of selective, segmental association into a compliant hydrogel mass on contact with an aqueous environment. In a preferred embodiment of the invention, the copolymer comprises a base component, designated xe2x80x9cComponent Axe2x80x9d herein. As used herein, the terms xe2x80x9cComponent Axe2x80x9d and xe2x80x9ccopolymer(s)xe2x80x9d are interchangeable and refer to the basic structure of the copolymers of the invention. Component A comprises a molecular chain having a hydrophilic block, designated xe2x80x9cYxe2x80x9d herein, and a relatively hydrophobic polyester block, designated xe2x80x9cXxe2x80x9d herein. Hydrophobic block X and hydrophilic block Y more preferably comprises a molecular structure having the following formula: X-Y-X or (X-Y)n, and branched structures thereof. Most preferably, hydrophobic block X comprises a polyester formed by grafting a glycolide, lactide, xcex5-caprolactone, p-dioxanone, trimethylene carbonate or combinations thereof, onto the hydroxylic or amino groups of a hydrophilic polymer precursor i.e., Y; hydrophilic block Y comprises a polyoxyethylene, poly(oxyethylene-b-oxypropylene), polypeptide polyalkylene oxamate, a polysaccharide, and derivatives thereof; or a liquid, high molecular weight polyether glycol interlinked with an oxalate or succinate functionalities in linear or branched form.
Component A optionally comprises carboxylic end-groups formed by any known technique in the art, such as, for example, end-group succinylation or glutarylation. This facilitates ionically binding a biologically active agent or drug to Component A, such that, drug release can be modulated. The biologically active agent or drug is preferably present on Component A in an insoluble form, such as, (I) a microparticulate dispersion, (2) a surface-deposited coating onto an absorbable microporous microparticles, and/or (3) ionically bound molecules onto the surfaces of absorbable microparticles which are preferably microporous that can be encased in an absorbable polymer to modulated its release further. The encasing can be achieved by allowing a dispersion of active micorparicle in solution of an absorbable polymer to phase separate by (a) solvent evaporation in with or without emulsion; (b) solvent exchange of nebulized microdroplets onto a precooled organic solvent such as, 2-propanol, which is a non-solvent for the polymer; (c) replacing the non-solvent in (b) with a supercritical fluid; or (d) replacing 2-propanol with a solution of water in an organic solvent.
In another embodiment of the invention, Component A optionally comprises an absorbable carrier associated therewith and, designated xe2x80x9cComponent Bxe2x80x9d herein. As used herein, the term xe2x80x9cassociated therewithxe2x80x9d refers to any chemical and/or physical means known in the art for combining components together. The function of Component B is to carry the biologically active agent. This is preferably desirable for medications which call for an initial drug burst and prolonged release thereafter and, thus, highly regulated availability of drugs at the biological site to modulate the release of the bioactive agent bound to component B, the latter may be encased in an absorbable polymer. The encased system can then be used as such for injection in an aqueous dispersion. In a further embodiment of the invention, encased Component B, having a bound bioactive agent such as, a peptide or a protein, is encased in an absorbable polymer as part of an aqueous pharmaceutical formulation for use in parenteral applications.
In a further embodiment of the invention, Component A, with or without component B and/or the biologically active agent, optionally comprises a similarly constituted low molecular weight block copolyester associated therewith. The low molecular weight coplyester preferably is a plasticizer and, more preferably, the plasticizer is designated xe2x80x9cComponent Cxe2x80x9d herein.
It is understood that Component A, with or without the biologically active agent/drug and/or compositions of Components A, B, C, the biologically active agent, and variations thereof, can provide a wide range of properties for treating a host of diseases, including, but not limited to, dental, ophthalmic, orthopedic and vascular applications. For example, the copolymers of the invention can: (1) be extruded or injected into living tissue or onto the surface of living tissues to provide a protective barrier to prevent post-surgical adhesion; (2) act as a blocking agent or sealant for treatment of defect in conduits such as blood vessels; (3) facilitate the controlled-release of a biologically active agent/drug for modulating cellular events such as wound healing and tissue regeneration or therapeutic treatment of cancer and diseases such as infection of the periodontium, eye, dry socket, bone, skin, vaginal, and nail infections; (4) facilitate the sustained in vitro or in vivo growth of viable cells and/or living tissues for the purpose of tissue engineering; (5) to aid in wound healing and augmentation; (6) to facilitate hemostasis; (7) to modulate the performance of tissue adhesives; and (8) to the healing of burns and ulcers.
The term xe2x80x9cHydrophobic Block(s)xe2x80x9d as used herein, refers to absorbable polyester chain block(s) or segment(s) of variable length which, is present in an isolated form, will produce practically amorphous (with less than 5% crystallinity) or totally amorphous material having a Tg of less than 25xc2x0 C., and preferably, is a viscous liquid at room temperature. Hydrophobic block(s) X comprises copolymeric segments of known chemistries in the art, such as, those comprised from cyclic lactones (e.g., glycolide, l-lactide, dl-lactide, xcex5-caprolactone, p dioxanone, trimethylene carbonate), polyalkylene oxalate, and the like, as described by Shalaby, 1988, cited elsewhere herein, which disclosure is hereby incorporated by reference. More preferably, hydrophobic segment(s) or block(s) X comprises lactide/glycolide copolymer (with 51 to 80% l- or dl-lactide).
The term xe2x80x9cHydrophilic Block(s)xe2x80x9d as used herein, refers to polymeric blocks or segments which, if present in an isolated form, will be water soluble. Hydrophilic block(s) or segment(s) Y comprises poly(oxyethylene), with or without a minor component of a higher homolog, such as, poly(oxypropylene)xe2x80x94polypeptide, polyalkylene oxamate (Shalaby et al., 1980, cited elsewhere herein, which disclosure is hereby incorporated by reference), a polysaccharide, or derivatives thereof. The length of the hydrophilic block and its weight fractions can be varied to modulate the rate of gel formation, its modulus, its water content, diffusivity of bioactive drug through it, its adhesiveness to surrounding tissue, and bioabsorbability.
The term xe2x80x9cHydrogelxe2x80x9d or xe2x80x9cHydrogel Massxe2x80x9d as used herein, refers to materials which have a high tendency for water absorption and/or retention, and maintain mechanical integrity through physical crosslinks which are reversible in nature.
The term xe2x80x9cPhysical Crosslinksxe2x80x9d as used herein, refers to a three-dimensional structure which is held together by physical quasi or pseudo crosslinks, or ionic bonds, as compared to covalently crosslinked. These physical crosslinks facilitate the reversibility of the hydrogel. This reversibility property can be influenced by external factors, such as, solvent or heat.
The term xe2x80x9cSelf-Solvatingxe2x80x9d as used herein, refers to components of chains which in the absence of external factors i.e., solvents, have greater affinity for physical interaction such that the components are capable of forming a virtually one phase system.
The term xe2x80x9cCompliantxe2x80x9d as used herein, refers to a material having a low modulus and which is easily deformable.
The term xe2x80x9cBiologically Active Agentxe2x80x9d as used herein broadly includes any composition or compound of matter which when dispensed in the chosen environment of use produces a predetermined, beneficial and useful result.
The term xe2x80x9cDrugxe2x80x9d or xe2x80x9cAgentxe2x80x9d as used herein broadly includes physiologically or pharmacologically active substances for producing a localized effect at the administration site or a systemic effect at a site remote from the administration site.
The term xe2x80x9cPlasticizerxe2x80x9d as used herein, refers to an absorbable polyester composition with hydrophilic and hydrophobic components similar, or identical to, those of Component A, with the exception of having a higher hydrophilic/hydrophobic ratio in Component C than Component A.
The term xe2x80x9cabsorbablexe2x80x9d means a water insoluble material such as a polymer which undergoes chain disassociation in the biological environment to water soluble by-products.
The term xe2x80x9cmicroparticlexe2x80x9d refers to the particles of absorbable polyester, which are preferably in essentially spherical form.
The term xe2x80x9cbound microparticlexe2x80x9d refers to a microparticle having one or more bioative agent(s)/drug(s), such as, peptide and/or one or more protein ionically immobilized on the microparticle.
The term xe2x80x9cencased microparticlexe2x80x9d refers to a bound microparticle having a polymer coating, where the polymer coating is not necessarily completely occlusive.
The term xe2x80x9cpolymer corexe2x80x9d is another way of referring to microparticles.
The term xe2x80x9cencasing polymerxe2x80x9d refers to the polymer that is used to encase a bound microparticle.
The term xe2x80x9cgel-forming liquid polyesterxe2x80x9d refers to materials which absorb solvents such as water, undergo phase transformation and maintain three dimensional networks capable of reversible deformation.
The present invention discloses novel hydrogel-forming, self-solvating, absorbable polyester copolymers, which upon hydration results in a hydrogel mass. The hydrogel mass is stabilized by pseudo-crosslinks provided by a hydrophobic polyester component, such as those comprised from cyclic esters e.g., glycolide, l-lactide, dl-lactide, F-caprolactone, p dioxanone, trimethylene carbonate, polyalkylene oxalate, derivatives thereof and the like, covalently linked to a hydrophilic component comprised of blocks, such as those derived from a polyethylene glycol, polypeptide, polyalkylene oxamate (U.S. Pat. Nos. 4,209,607 and 4,226,243, to Shalaby et al., hereby incorporated by reference), or polysaccharide and derivatives thereof. The polyester copolymers, with or without modifying additives, undergo hydration in the biologic environment leading to selective segmental association thereby forming compliant hydrogels at the application site.
These copolymers are especially useful for localized, controlled delivery of biologically active agents/drugs and protecting or augmenting damaged, compromised, and/or traumatized tissues. More particularly applications of the novel copolymers of the invention include: (a) the treatment of periodontal disease, wherein a tetracycline-, doxycycline- or chlorhexidine-containing hydrogel-former is injected in the periodontal pocket to form an adhesive gel or semi-solid mass in the pocket for the controlled release of such antimicrobial drugs over a period of 2 to 45 days. Near the practical exhaustion of the drug, the polymer will commence to absorb and/or disintegrate substantially as it undergoes advanced stages of degradation; (b) the prevention and treatment of dry socket with formulations similar to those of Component A; (c) providing a hydrogel barrier with or without non-steroidal anti-inflammatory drugs or agents which prohibit fibrotic tissue production on traumatized tissue to prevent post-surgical adhesion; (d) applications as an antimicrobial hydrogel for the treatment of vaginal infections; (e) treatment of bone diseases such as osteomyelitis, with injectable formulations comprising antibiotics including gentamicin and vancomycin; (f) accelerating tissue regenerating in compromised soft and hard tissue, e.g., fractured bone, ulcers, burns, by employing formulations comprising growth promoters, such as growth factors or their oligomeric analogs; and, (g) treatment of diseases such as psoriasis and infected nails using formulations comprising antimicrobial agents. Other applications of the hydrogel-forming copolymers of the invention include (a) blood vessel sealant; (b) vascular blocking agent; (c) carrier for injectable anti-inflammatory formulations in the treatment of joint diseases; (d) active carrier of viable cells or living tissue; (e) carrier for dispensing anti-cancer agents, which may be a peptide or protein or mixtures thereof; (f) hemostatic agent; (g) aid to ligating devices such as surgical staples and sutures; and (h) tissue adhesive.
The copolymers of the invention comprise a primary or base component designated xe2x80x9cComponent Axe2x80x9d herein. Component A comprises molecular chains having a hydrophilic block, designated xe2x80x9cYxe2x80x9d herein, and a relatively hydrophobic polyester block, designated xe2x80x9cXxe2x80x9d herein. The molecular structure of hydrophobic block X and hydrophilic block Y preferably comprises one of the following formulas: X-Y-X or (X-Y)n, and branched structures thereof. More preferably, hydrophobic block X comprises a polyester formed by grafting a glycolide, lactide, xcex5-caprolactone, p-dioxanone, trimethylene carbonate or combinations thereof, onto the hydroxylic or amino-end groups of a hydrophilic polymer precursor i.e., Y. Hydrophilic block Y preferably comprises a polyoxyethylene, poly(oxyethylene-b-oxypropylene), polypeptide, polyalkylene oxamate, a polysaccharide, or derivatives thereof, or a liquid, high molecular weight polyether glycol interlinked with oxalate or succinate functionalities in linear or branched form.
In a preferred embodiment, Component A comprises a polyethylene glycol having a molecular weight of about 400 Daltons which is pre-interlinked with succinate or oxalate bridges to increase the length of the hydrophilic block and, thus, the molecular weight of A without favoring its crystallization. That is, the hydrophilic prepolymer xe2x80x9cYxe2x80x9d having hydroxylic end-groups, is end-grafted with a mixture 60/40 dl-lactide/glycolide to produce a block copolymer having a hydrophilic block fraction xe2x80x9cYxe2x80x9d of about 0.25. To render Component A more receptive to basic drugs, its end-groups can optionally be carboxylated, for instance, by their acylation with succinic anhydride. Component A, with or without a biologically active agent, is introduced to a biological target site using conventional means and, thereafter, undergoes selective-segmental segregation to form a flexible, compliant, reversible gel which adheres to the surrounding tissues and acquires the configuration of the site. Component A of the invention more preferably comprises an inherent viscosity at 25xc2x0 C. in chloroform ranging between 0.03 to 0.80 dL/g and can be present as a liquid at room temperature, or practically amorphous material (with less than 5% crystallinity) with a Tg of less than 25xc2x0 C., which can be extruded through a die or administered through a syringe needle.
Component A comprises copolymeric chains with self-solvating components (analogous to phase mixing of two component miscible blends) to allow its existence as a viscous, extrudable material at room temperature, and its transformation to a flexible reversible hydrogel upon administration to a biological site. These hydrogels adhere tenaciously to adjacent tissues and acquire the shape of the site. The present copolymers are mechanically compatible in highly sensitive sites, as well as, can mediate external mechanical stresses or shocks. As such, the copolymers of the invention can be applied easily without incorporating a major extrinsic water-soluble, potentially cytotoxic organic solvent in order to facilitate upon administration in-situ coagulation to a solid mass.
Component A, with or without a bioactive agent/drug, such as, non-steroidal anti-inflammatory drug (NSAID) or active polypeptide, can be used as a protective barrier, a blocking agent of vascular defects caused by needle puncturing, a sealant of damaged surfaces for preventing post-surgical adhesion or as a carrier of immunostimulants or viable cells. Component A, mixed with an antimicrobial agent/drug, can be injected or applied topically with a suitable known applicator for the treatment of bone, cartilage, nail, skin, and vaginal infections.
In another embodiment of the invention, Component A optionally includes a biologically active agent/drug, such as, an antimicrobial agent, anesthetic agent, antibiotic, and/or a peptide or protein, for regulating cellular events. The biologically active agent/drug can comprise by way of illustration, antifungal agents, antibacterial agents, antibiotics, anti-inflammatory agents, anti-cancer agents, immunosuppressive agents, immunostimulatory agents, dental densitizers, odor masking agents, immune reagents, anesthetics, antiseptics, nutritional agents, antioxidants, lipopolysaccharide complexing agents, prostaglandin analog, cisplatin, peroxides, tissue growth factors, a mixture of any of the foregoing, and the like. The agent/drug can be deposited, wholly or in part, on Component A, with or without carboxy-terminated ends. In an alternative embodiment, the biologically active agent/drug can be deposited, wholly or in part, on a solid carrier, designated xe2x80x9cComponent Bxe2x80x9d herein. Component B preferably is an absorbable, powder prior to mixing with Component A. More preferably, Component B is an absorbable, microporous low molecular weight polyester which is highly crystalline and practically insoluble in Component A or, Component B with the active agent, is encased in a less absorbable polymer to modulate the release of the bioactive agent.
A preferred formulation of Components A/B comprises a mixture of 20/80 B/A, with B being a low molecular, microporous polyglycolide with 0.70 to 0.95 solid fraction, average particle size of 0.5-200 micron and carboxyl-bearing chains. High concentration of carboxylic groups on the chains can be achieved by preparing Component B using di- or poly-carboxylic acid as initiators such as malic, citric and tartaric acid. The deposited agent on Component B can exhibit a release profile which can be multiphasic, including: (a) simple, fast diffusion of soluble free drug through gel A; (b) slow diffusion of soluble free drug housed in the pores of B; and, (c) drug release at the surface (both exterior and pore) of B or the chain ends of carboxylated A chains by ion exchange of ionically bound molecules. To modulate the release of active agents, such as amino-acids, peptides or proteins that are bound to Component B, the entire system may be encased in an absorbable polymer, This can be used in conjunction with Component A or a dispersion in an aqueous pharmaceutical formulation for parenteral administration. For anionic drugs, Component B can be chemically modified to reverse its available charge to perform as an anion-exchanger for binding carboxyl-bearing bioactive agents. Similar to the cation-exchanging microparticles, the anion-exchanger can be used in an encased or unencased form in an aqueous dispersion or a non-aqueous gel-former.
By varying the concentration of Component B in Component A, the flow characteristics and release profile of the agent can be modulated. This is important because in certain applications, the flow characteristic or properties of Component A/B formulations can determine the clinical efficacy, particularly in cases of treating periodontal disease, nail infection and bone infection where high viscoelasticity (due to the high weight fraction of the micro-particulate dispersed phase and its physicomechanical interlocking with viscous liquid continuous phase A) of the gel composite is pertinent to assure mechanical stability at the target site.
Component A optionally includes an absorbable low molecular weight component. This component can modulate the rheological properties, gel-formation time, and mechanical disposition of Component A at the target site. The low molecular weight component preferably is a plasticizer and, more preferably, the plasticizer is designated xe2x80x9cComponent Cxe2x80x9d herein. Component C can (a) aid the dispersion of Component B in Component A; (b) reduce the overall system viscosity of Component A/B formulation, (c) contribute to reducing the viscosity and facilitating the injectability of Component B if used alone or with a biologically active compound, and/or (d) increase the rate of hydration or gel formation. The absorbable plasticizer, such as Component C, is capable of modulating the viscosity and/or gel-formation rate of Component A, with or without Component B, thereby broadening its applicability. Highly viscous forms of Component A can be easily plasticized with a low molecular weight (inherent viscosity of 0.03-0.15) polyester copolymer Component C, that is made of the same or physically compatible chemical entities as Component A, (but different hydrophilic weight fraction) to produce easily injectable liquid systems.
In a more preferred embodiment, Component A is formed by end-grafting a polyethylene glycol having a molecular weight of about 400-900 Dalton with a mixture of glycolide and l- or dl-lactide in the presence of stannous octoate as a catalyst to produce a block copolymer with (a) ether/ester mass ratios of 20-49/80-51, preferably 25-40/75-55 and, most preferably 30-40/70-60; (b) having an inherent viscosity in chloroform at 25xc2x0 C. from about 0.03 to 0.80, preferably from about 0.1 to 0.6, more preferably from about 0.15 to 0.5, and most preferably from about 0.2 to 0.4 dL/g; and (c) is in the form of an extrudable, essentially amorphous, semi-solid having a Tg of less than 25xc2x0 C., preferably an amorphous material having a Tg of less than 37xc2x0 C., and more preferably a viscous liquid at room temperature that can be easily administered through a syringe needle.
In a still more preferred embodiment, copolymer Component A is formed by end-grafting an oxalate-, succinate- or glutarate-interlinked liquid polyethylene glycol having a molecular weight of more than 1200 Dalton with a mixture of glycolide and l- or dl-lactide in the presence of stannous octoate as a catalyst to produce a block copolymer with (a) ether/ester mass ratio of 20-49/80-51 and preferably 25-40/75-55 but most preferably 30-40/70-60; (b) having an inherent viscosity in chloroform at 25xc2x0 C. of about 0.03 to 0.80, preferably 0.1 to 0.60, more preferably, 0.15 to 0.50, and most preferably, 0.2 to 0.4 dL/g; and (c) in the form of extrudable, essentially amorphous semi-solid having a Tg of less than 25xc2x0 C. and preferably an amorphous material having a Tg of less than 25xc2x0 C. and, more preferably, a viscous liquid at room temperature that can be easily administered through a syringe needle.
Formulations comprised of the polyester-alkylene carbonate copolymers of the invention are suitable carriers of biologically active agents/drugs at typical loading levels of about 0.02 to 20%. The chain of Component A or Component C can be succinylated to provide acidic end-groups for ionic binding of the agents/drugs. Liquid compositions made of Component A or Components A/C, with or without agent/drug, can form hydrogels upon contacting a liquid environment. This is achieved through the hydration of the hydrophilic block of the copolymeric chains leading to intramolecular conformational changes and association of the hydrophobic blocks (or segments) as pseudo-crosslinks in a reversible, hydrophilic/hydrophobic hydrogel system.
For copolymer formulations comprising the agent, such morphology provides a suitable environment for the controlled release of the agent. The agent can be present in a soluble or dispersed form. Preferably, the agent is deposited on a micronized powder, more preferably a microporous absorbable powder and, most preferably, a powder (Component B) which offers an ion-binding, high surface area for ionically immobilizing part of the soluble agent to control its release and, thus, produce copolymers with a multiphasic release profile over a period of 2 to 60 days. To prolong release further for up to 3 or 6 months, the micorparticulate with the immobilized active agent may be coated or encased with a slow-absorbing polymer. This may be used in a parenteral aqueous formulation or non-aqueous gel-forming system (e.g., Component A).
More specifically, the biologically active agents can be present as (a) a solute in Component A; (b) a dispersed solid in Component A; (c) a coating on Component B; (d) ionically bound molecules on Components A and/or B; and/or (e) mechanically held within the pores of Component B. Each of these forms of drug will have its own release pathway and, thus, bio-availability at the site. Depending on the concentration of Component B, the hydrogel-forming formulation can be made to have a broad range of properties and gel-formation kinetics to allow its use in many applications.
Component A with a biologically active agent and/or Components B and/or C, is used for treatment of periodontal disease, osteomyalitis, and dry socket. While a discussion follows for using the copolymers of the invention for treatment of periodontal disease, it is understood that this discussion is for purposes of illustration only and, not limitation, and the copolymers of the invention have broad applications of use. Periodontal disease, as used herein, is a general term for a number of diseases that affect the periodontal tissue. These diseases are characterized by a range of symptoms including inflammation, bleeding, exudation of pus from the gingival sulcus, deepening of the sulcus to form periodontal pockets, tissue lesions, loss of connective tissue, alveolar bone loss, and ultimately tooth loosening and loss. The primary cause of periodontal disease is now believed to be bacterial infection of the plaque that forms on tooth surfaces below the gingival margin. The copolymer formulations of the present invention are useful for prolonged, controlled dispensing of a range of drugs and agents, such as, for example: (a) prophylactic prolonged application of minerals and ions, such as calcium or fluoride ion; (b) prolonged controlled exposure to local antiseptics, including, chlorhexidine and tibezonium iodide; (c) controlled antibiotic delivery, including such antibiotics as aminoglycosides, macrolides such as erythromycin, penicillins, cephalosporins and the like; (d) anesthetic/analgesic delivery pre- or post surgery or to treat other mouth pain using such agents as amide-type local anesthetics like lidocaine, mepivacaine, pyrrocaine, bupivacaine, prilocaine, etidocaine, or the like; (e) local controlled delivery of non-steriodal anti-inflammatory drugs such as ketorolac, naproxen, diclofenac sodium and fluribiprofen; and (f) local controlled release antiviral agents (e.g., acyclovir and ganciclovir), immuno-suppressants (e.g., cyclosporin), anti-glaucoma drugs and anti-cancer drugs (interferon and somatostatin analogs). It is recognized that in certain forms of therapy, combinations of agents/drugs in the same delivery system i.e., copolymer of the invention, can be useful in order to obtain an optimal effect. Thus, for example, an antibacterial and an antiinflammatory agent may be combined in a single copolymer to provide combined effectiveness.
It has also been recently shown that regrowth and repair of periodontal connective tissue can be encouraged with the aid of polypeptide mitogenic growth factors. See, for example, V. P. Terranova et al., Biochemically Medicated Periodontal Regeneration, J. Periodont. Res., 22, pages 248-251, incorporated herein by reference. The copolymers of the present invention can be designed to release appropriate encapsulated, or uncapsulated, growth factors, including, epidermal growth factors, human platelet derived TGF-B, endothelial cell growth factors, thymocyte-activating factors, platelet derived growth factors, fibroblast growth factor, fibronectin or laminin.
The drug/agent can be used at a level of from about 0.1% to a about 70%, preferably form about 1% to about 50%, most preferably form about 2% to about 30%. The copolymers of the invention can be designed to release drug to provide a steady state number average concentrations of from about 1 xcexcg to about 2000 xcexcg, preferably form about 20 xcexcg to about 1200 xcexcg, most preferably from about 50 xcexcg to about 800 xcexcg per milliliter of the gingival crevicular fluid of a treated periodontal pocket. The steady state release rates can be altered by varying component ratios of the copolymer formulations. The steady state conditions are preferably used since initial bursts are accounted for as well as delays in release. For example, in the case of a ten (10) day therapy, steady state is generally reached in about one to two days. More preferably, a formulation for treating periodontal disease comprises 20/80 Components B/A, containing 1-3% of an active drug such as chlorhexidine or tetracycline.
In addition to the agent/drug, the copolymer formulations of the present invention can include a variety of optional components. Such components include, but are not limited to, surfactants, viscosity controlling agents, medicinal agents, cell growth modulators, dyes, complexing agents, antioxidants, other polymers such as carboxymethly cellulose, gums such as guar gum, waxes/oils such as castor oil, glycerol, dibutyl phthalate and di(2-ethylhexyl) phthalate as well as man others. If used, such optional components comprise form about 0. 1% to about 20%, preferably from about 0.5% to about 5% of the total copolymer formulation
The copolymers of the invention can be inserted into the periodontal pocket or gingival region, and can be administered in the form of a particle, film or sheet. The size, shape and thickness can be changed according to the condition of the disease to be treated. Ordinarily, the size, shape and thickness are changed according to the size of the periodontal pocket of the patient or the condition of the gingiva.
In another embodiment of the invention, there is contemplated pharmaceutical formulations comprising the copolymers of the invention. For example, a preferred pharmaceutical formulation comprises an injectable viscous fluid of Component A, Components A/B, Components A/B/C and/or Components A/C, containing about 0.01% to 10% agent/drug and, more preferably about 0.2% to 5% of agent/drug. The released of the agent/drug is over a period of 1 to 60 days and, more preferably 7 to 45 days. The drug/agent can include anti-microbials, such as, chlorhexidine, tetracycline, doxycycline and metronidazole; antibiotics, such as, gentamicin and vancomycin; and compounds which can accelerate wound healing or tissue regeneration, prevent post-surgical adhesion, neoplastic formation, and prevent or accelerate blood clotting.
In another embodiment of the pharmaceutical formulation, the copolymer comprises part or all of the bioactive agent deposited on a microporous and/or finely divided absorbable powder, such as, those consisting of low molecular weight crystalline polyglycolide or copolyglycolide. The powder is formed by low to moderate conversion (that is 60-95%) ring-opening polymerization of glycolide or a mixture made predominantly of glycolide and small amounts of other lactones. The polymerization is carried out in the presence of stannous octoate as a catalyst and sufficient concentration of glycolic acid as an initiator to produce a mass. Upon quenching, grinding, roll-milling in an inert medium, and extraction with water, 2-propanol, microporous particles are produced having (a) 1 to 200xcexc diameter and, more preferably 5-75xcexc; (b) an inherent viscosity in hexafluoro-2-propanol at 25xc2x0 C. of  less than 0.03 to 0.3 and, more preferably  less than 0.05 to 0.2 dL/g; (c) contain less than 2% residual monomer; and (d) have 0.03 to 0.35 and, more preferably 0.05 to 0.25 pore fraction. For encasing the microparticles with an absorbable polymer, a lactide polymer based on 60 to 100 lactide residues may be used.
In another embodiment, the pharmaceutical formulation consists of Component A with or without Component C and preformed microspheres (or microcapsules) of the bioactive agent/drug in an absorbable polymer.
An important difference between conventional formulations in the art and the novel copolymers of the invention, is that the present copolymers do not include the use of organic solvents. Such solvents can compromise the copolymers shelf-stability, as in the case of a polyester in a basic solvent such as N-methyl-pyrrolidine, which can catalyze chain dissociation in the presence of trace amounts of moisture. The prior art formulations also teach the use of other reactive solvents such as propylene glycol (which degrades the polyester chain through alcoholysis), or trimethylene carbonate (which can copolymerize with the polyester chain). Moreover, should the prior art formulations be radiation sterilized, the presence of a solvent can lead to the generation of new chemical species originating from the solvent as well as in combination with the bioactive ingredient. In effect, organic solvents described in the prior art can compromise the purity and efficacy of both the drug (optional) and polymer which can, in turn, be associated with unsafe use.
Another feature of the novel copolymers of the invention, is that when administered to a biological site the copolymers do not experience discernible reduction in organic mass, as is the case of prior art compositions which coagulate in-situ by leaching out a major water-soluble component. Leaching out a major water-soluble components can be associated with shrinkage and separation from the surrounding tissue and, in some instances, uncontrolled formation of microporous mass. Because the copolymers of the invention are comprised of copolymeric chains, the copolymers can be easily tailored to modulate its viscosity without the intervention of a new chemical species, such as, an organic solvent.
A further feature of the novel copolymers of the invention, is that since the copolymers are comprised of self-solvating molecules, its conversion to a hydrogel about a drug provides a uniform distribution of the therapeutic agent, and thus, more reproducible release profile, in contrast with prior art systems where complex physical events prevail due to the presence of leachable solvents.
A microparticle of the present invention is crystalline and is made of an absorbable polyester, such as polyglycolide having one or more carboxylic groups on the individual chains which results in a sufficient concentration of carboxylic groups on the surface of the microparticle and immediate subsurface of the microparticle to complex and ionically immobilize a peptide(s) and/or a protein(s) having one or more basic groups. Or the carboxylate groups of the polyglycolide can be amidated, for example by a diamine, preferably a primary or secondary amine or a mixture thereof, wherein the amine forms a complex that ionically immobilizes a peptide(s) and/or a protein(s) having one or more acidic groups. Since the surface of the microparticles is not necessarily homogeneous, the term xe2x80x9csubsurfacexe2x80x9d refers to the crevices and the like found on the surface of the microparticles. The bound microparticles provide a means for the controlled release of a peptide(s) and/or protein(s) in a patient. To further control the release of the immobilized peptide(s) and/or protein(s), the bound microparticles can be encased individually or in groups with an absorbable polymer coating. The bound microparticles release the peptide(s) and/or protein(s) over a period of about two days to about three months in a patient, preferably about one week to about three months. The encased microparticles release the peptide(s) and/or protein(s) over a period of about three days to six months in a patient, preferably about two weeks to five months.
A microparticle can be made of a lactide based polymer or a solid semi-crystalline polylactone such as polyglycolide which can be formed by ring opening polymerization of acid-bearing hydroxylic initiators such as glycolic, lactic, malic, tartaric, and citric acid. A microparticle of the present invention can be synthesized according to the following procedure. In a reaction vessel are mixed a lactide based monomer and/or a lactone such as glycolide and an acid initiator such as tartaric acid, malic acid or citric acid. The reaction vessel is warmed to about 35-45xc2x0 C., preferably 40xc2x0 C. and put under vacuum for about 20-60 minutes, preferably 30 minutes. The temperature of the reaction vessel is raised to about 105-115xc2x0 C., preferably 110xc2x0 C. Once this temperature is reached the vessel is placed under an atmosphere of oxygen-free nitrogen, and the mixture is stirred. Once the mixture melts, a catalytic amount of an organometallic catalyst suitable for ring opening polymerization, such as stannous 2-ethyl-hexanoate solution in a non-protic solvent, such as toluene is added. A vacuum is reapplied for about 30-90 seconds to remove toluene without significant removal of monomer. The temperature of the mixture is raised to about 115-125xc2x0 C., preferably 120xc2x0 C. for about 5-10 minutes before further raising it to about 145-150xc2x0 C. It was kept at this temperature for about 3-5 hours, preferably 4 hours, under constant mechanical stirring, if possible.
The resulting polymer is micronized by initially grinding it using a Knife-grinder. The polymer is then micronized in an Aljet Micronizer using a pressurized dry nitrogen stream. The mean particle diameter size is analyzed in a Malvern Mastersizer/E using a volume distribution model and 200/5 cS silicone oil as dispersant.
The polymer is purified and the sodium salt thereof is formed first by dispersing the micronized polymer in acetone and placing it in a sonicator, preferably for about 30 minutes. During this time the dispersion was also homogenized at about 8,000-24,000 rpm, preferably 9,500 rpm, using a homogenizer. After this sonication/homogenization step the dispersion is centrifuged at about 3,000-7,000 rpm, preferably 5,000 rpm _preferably for about 30 minutes in a centrifuge. The supernatant is discarded, the centrifuge cakes re-suspended in fresh acetone, and the sonication/homogenization step repeated. Once the second centrifugation is complete, the supernatant is discarded and the cakes were re-suspended in deionized water. One final sonication/homogenization step is then carried out to remove any remaining acetone and the dispersion is once again centrifuged at about 5,000 rpm for about 30 minutes.
The centrifuge cakes are re-suspended in fresh deionized water and the pH of the dispersion is monitored. Sufficient volumes of a weak base such as 0.2M sodium carbonate solution are added with stirring to raise the pH to between about pH 8 and about pH 9. The dispersions are allowed to stir for about 30 minutes before being vacuum-filtered over filter paper. The filter cakes are rinsed with further deionized water, frozen, and lyophilized.
Purification is monitored by differential scanning calorimetry (DSC) with a heating rate of about 5xc2x0 C./min. to 15xc2x0 C./min., preferably 10xc2x0 C./min.
An anion-exchanger microparticle is obtained by taking the cation-exchanger microparticles and incubating it in hot dilute solution (xcx9c80xc2x0 C. -100xc2x0 C.) of a diamine, it is preferred that the amines can be both a primary amine or both a secondary amine or a mixture of a primary and a secondary amine, of known concentration in dioxane or toluene under an inert gas such as argon. The concentration of the diamine in dioxane or toluene is determined by acidimetry. When the reaction practically ceases to take place, the amidated microparticles are separated by filtration, rinsed with dioxane or toluene, and dried under reduced pressure.
A peptide(s) and/or protein(s) can be immobilized on a microparticle according to the following method. The sodium salt of a microparticle is dispersed in solutions containing the cationic form of a peptide(s) and/or protein(s) dissolved in water. The dispersions are incubated at room temperature with stirring for about 2 hours before filtering out the bound microparticles. The filter cakes are rinsed with further deionized water, frozen, and lyophilized. Samples are then analyzed for nitrogen by elemental analysis to determine the amount of the peptide(s) and/or protein(s) immobilized.
The size of a microparticle plays a role in the amount of a peptide and/or protein that a microparticle of the instant invention can immobilize. The smaller the size of a microparticle, the more surface area a mass of microparticles possess and, thus, the more peptide and/or protein can be immobilized per unit mass of microparticles. Size reduction of the microparticles to micron or sub-micron dimensions can be achieved as described above. The diameter of the microparticles can range in size from about 0.5 xcexcm to 100 xcexcm, preferably 10 m to 80 xcexcm and more preferably 20 xcexcm to 70 xcexcm.
The absorbable encasing polymer can be a crystalline or non-crystalline lactide/glycolide copolymer, amorphous l-lactide/d,l-lactide co-polymer, caprolactone/glycolide copolymer or trimethylene carbonate/glycolide copolymer, that is soluble in conventional organic solvents, such as chloroform, methylene chloride, acetone, acetonitrile, ethyl acetate, and ethyl formate. Non-solvents of such an absorbable encasing polymer include water, aqueous or non-aqueous, low boiling temperature alcohols and supercritical fluids. The absorbable encasing polymers can be synthesized by catalyzing ring-opening polymerization of cyclic or heterocyclic monomers such as xcex5-caprolactone, p-dioxanone, trimethylene carbonate, 1,5-dioxepan-2-one or 1,4-dioxepan-2-one or mixtures thereof in the presence of a chain initiator, such as a hydroxylic compounds, such as propanediol.
The encasing of the bound microparticles can be achieved by phase separation of an emulsion. An alternate encasing method entails the use of an ultrasonic atomizer where a dispersion of the bound microparticles in an absorbable encasing polymer solution is introduced as micro-droplets into a cooled non-solvent medium. Bound microparticles are encased with an absorbable encasing copolymer of lactide and glycolide using traditional microencapsulation or coating techniques of solid particles such as the emulsion evaporation method described by H. Demian and S. W. Shalaby for encapsulating barium sulfate microparticles as disclosed in U.S. Patent application U.S. Ser. No. 08/467,361, the contents of which are incorporated herein by reference, or by coagulation of solid microparticles encased in a polymer solution and delivered through an ultrasonic atomizer (nebulizer) into a liquid medium that is a non-solvent for the encasing polymer, but where the liquid medium non-solvent is capable of extracting the solvent of the encasing polymer solution about the encased solid microparticles. Depending on the concentration of the polymer solution for encasing the microparticles, the number of the original bound microparticles in the encased microparticles can vary from 1 to several hundred with an average diameter of an encased microparticle ranging from 0.5 xcexcm to 100 xcexcm.
The following method relates to the preparation of encased peptide- and/or protein-loaded (hereinafter peptide-loaded) cation exchangers by nebulization. The encasing copolymer of interest is dissolved in a solvent, such as either acetonitrile, ethyl acetate or ethyl formate at a concentration of between 10 and 30% (W/W). A sufficient weight of this solution is used for dispersion of the peptide-loaded CE so that the weight ratio of peptide-loaded CE to encasing copolymer ranges from about 30:70 to about 80:20. Dispersion is achieved by high speed homogenization. The dispersion is fed at a flow rate of between 1 ml/min and 10 ml/min to an ultrasonic atomization nozzle with variable frequencyxe2x80x94this frequency can be altered from 12kHz to 35kHzxe2x80x94higher frequency allows higher flow rates while maintaining particle characteristics. The dispersion is thus nebulized into a collecting sink made up of at least 1 to 10 times excess of isopropyl alcohol (IPA) or ethanol (compared to the volume of encasing copolymer solvent used) containing sufficient dry-ice so that the temperature of the slurry remains between xe2x88x9277xc2x0 and xe2x88x9280xc2x0 C. throughout the nebulization. This slurry is stirred at more than 100 rpm depending on its volume. In the case of acetonitrile as solvent, the nebulization droplets will freeze immediately on contact with the slurry. Once nebulization is complete the entire dispersion is allowed to thaw of its own accord to between 10xc2x0 C. and room temperature before vacuum filtering. The filter cakes are rinsed with de-ionized water to remove excess non-solvent. The particles obtained have the appearance of smooth microspheres in the case of a predominantly d,l-lactide encasing copolymer; they appear slightly wrinkled when the encasing copolymer is mainly I-lactide based. In an alternative process, the encasing is achieved using a supercritical fluid, such as, CO2 as the non-solvent.
The binding capacity of a microparticle ion-exchanger can be determined as follows. For example, for a cation-exchanger microparticle, available carboxylic groups, in a predetermined mass of the microparticles, are neutralized using cold dilute aqueous sodium carbonate solution of known normality. The neutralized microparticles are isolated by filtration and rinsed thoroughly with cold deionized water and then air dried. The solid microparticles are then incubated in dilute solution of Pilocarpine hydrochloride of known concentration so as to provide a slight excess of the basic drug over that predicted from the neutralization data. The concentration of the remaining Pilocarpine HCl in the aqueous medium is monitored for a period of time until no significant change in the base pick-up by the microparticles can be recorded. The percent of immobilized base on the microparticles is determined from the exhaustion data and then verified by elemental analysis for nitrogen.
The binding capacity of the anion-exchanger (amidated particles) is determined by (1) elemental analysis for nitrogen and (2) extent of binding to Naproxen by measuring the extent of Naproxen removed from a dilute solution using HPLC. The latter is confirmed by release of the immobilized Naproxen with a dilute sodium hydroxide solution of known concentration.
The bound microparticles or the encased microparticles of this invention can be administered to a patient via administration routes well known to those of ordinary skill in the art, such as parenteral administration or oral administration. Preferably it is administered as a powder or a suspension via intranasal route or as an inhalant through the pulmonary system. When it is administered parenterally it is preferable that it is administered as a dispersion in an isotonic aqueous medium or in a non-aqueous, absorbable gel-forming liquid polyester.
The effective dosages of bound microparticles or encased microparticles to be administered to a patient can be determined by the attending physician or veterinarian and will be dependent upon the proper dosages contemplated for the peptide(s) and/or protein(s) and the quantity of the peptide(s) and/or protein(s) immobilized on the microparticles. Such dosages will either be known or can be determined by one of ordinary skill in the art.
The preparation of gel-formers is disclosed in U.S. Pat. No. 5,612,052, the contents of which is incorporated herein by reference. Specific examples of gel formers are described below.
Preparation of 80/20 (by weight) Block Copolymers of 60/40 Trimethylene Carbonate/Glycolide and Polyethylene Glycol-400 (GF-1): A flame-dried resin kettle equipped with a mechanical stirrer and a nitrogen inlet was charged with polyethylene glycol-400 (0.299 mole, 119.5 g), stannous octoate (0.2 M in toluene, 4.700 ml, 0.946 mmole), glycolide (1.78 mole, 206.5 g) and trimethylene carbonate (2.65 mole, 270 g). The reactor was purged with argon several times and then heated to melt and then heated to and stirred at about 150xc2x0 C. for about 12 hours. At the conclusion of the reaction, the temperature was lowered while maintaining fluidity and excess monomer was removed under reduced pressure. The resulting polymer was analyzed by infrared and NMR for composition and gel-permeation chromatography for molecular weight.
Preparation of 15/85 (by weight) Block Copolymer of 60/40 Trimethylene Carbonate/Glycolide and Polyethylene Glycol-400 (GF-2): The title copolymer was synthesized according to the procedure described for GF-1 but using polyethylene glycol-400 (1.063 mole, 425 g), stannous octoate (0.2 M in toluene, 1,760 ml, 0.35 mmole), glycolide (0.279 mole, 32.4 g) and trimethylene carbonate (0.418 mole, 42.6 g) and stirring for about 9 hours.
Preparation of 80/20 (by weight) Block Copolymer of 90/10 Trimethylene Carbonate/Glycolide and Polyethylene Glycol-1500 (GF-3): The title copolymer was synthesized according to the procedure described for GF-1 but using polyethylene glycol-1500 (0.267 mole, 400 g), stannous octoate (0.2 M in toluene, 1200 ml, 0.247 mmole), glycolide (0.097 mole, 11.2 g) and trimethylene carbonate (0.87 mole, 88.7 g) and stirring for about 13 hours.
The following Examples are provided to further illustrative the present invention, and should not be construed as limitations thereof: